When you look at your roof from afar, you can easily picture rows of solar panels perched neatly on top, soaking up the sun. But when you think about how many can actually fit – especially with things like valleys across the slope or a dormer sticking up – it’s not always so clear. In this article, I’ll walk you through how to figure out how many solar panels can fit on your roof, and how much energy it can potentially generate, so you can truly understand how solar can work for you.
How Many Solar Panels Can Fit On My Roof?
How many solar panels you can fit on your roof depends primarily on your roof’s usable space and the dimensions of the solar panels you plan to install.
At a glance, it looks like a matter of simple division – divide the roof size by the panel’s dimensions. A 1,600 square-foot roof (the average roof size according to data from the Angi website) could fit about 91 average-sized solar panels measuring 17.5 square feet each…
But this approach isn’t entirely practical. Bear in mind that roof size doesn’t always equal ‘usable space’. Rather, usable space is your roof area minus certain factors that can limit your installation, such as:
- Obstructions like chimneys, vents, skylights, and other features that take up space
- Roof irregularities including valleys, ridges, and multi-level designs that complicate panel placement
- Shading from trees, nearby buildings, or other objects that may reduce the amount of sunlight reaching your panels
- Clearance needed from the roof’s edges and apex, typically 8 to 16 inches, to prevent wind uplift and allow for maintenance
With that said, here’s a more accurate way to calculate how many solar panels you can fit on your roof:
Step 1: Measure Your Roof’s Usable Space
Start by measuring the total area of your roof. Then adjust for obstructions, irregularities, shading, and clearance requirements to calculate the usable space.
Step 2: Know the Size of the Solar Panels You’ll Buy
Solar panel sizes vary by brand and model. You can check the manufacturer’s website for the specific measurements of the panels you intend to purchase.
If you’re simply aiming for a quick back-of-the-envelope calculation, know that residential panels typically measure around 5.4 ft by 3.25 ft (17.5 square feet).
Step 3: Calculate the Number of Panels
Once you know your roof’s usable area, divide it by the size of one panel.
If your roof has 350 square feet of usable space, for example, you can fit approximately 20 panels (350 ÷ 17.5 = 20). Bear in mind that this is just an estimate, and factors like your panel’s layout and spacing can affect the final number.
How Much Solar Power Can My Roof Generate?
When you’ve sorted out how many panels your roof can accommodate, your next question will likely be, “How much power can they produce?”. Having been in the solar industry for several years, here are the key factors homeowners should consider when calculating their solar energy generation potential.
Solar Panel Power and Efficiency
Beyond the quantity of your solar panels, each panel’s power output or wattage greatly influences how much energy you can yield.
Most residential panels generate between 250 and 400 watts. If you have 20 panels with an average output of 250 watts each, your system’s total capacity would be 5,000 watts (250 x 20) or 6 kilowatts (kW)…
If you have 400-watt panels instead, you’ll generate more power in the same amount of space – 8 kW to be exact.
On top of wattage, efficiency also matters. This is basically your panels’ ability to convert sunlight into power. Most panels stand at 19% efficiency, although much newer models could reach up to 24% efficiency.
Peak Sunlight Hours
The amount of energy your system produces also depends on how much sunlight your area receives. If your location gets an average of 5 peak sunlight hours per day, a 6 kW system can generate about 30 kWh (6 kW x 5 hours) daily.
Bear in mind that sunlight hours vary by season. In Utah, for example, June (summer) sees nearly 8 peak sunlight hours per day, but this drops to just 2.5 hours in December (winter), based on NREL data.
Accounting for these seasonal changes would give you a more accurate estimate of your system’s annual production.
Roof Orientation and Tilt
Orientation refers to the direction your roof faces – north, south, east, or west. Solar panels mounted on south-facing roofs receive the most consistent and direct sunlight throughout the day and across seasons.
East- and west-facing roofs still capture sunlight but generally produce less energy since they only capture light during specific parts of the day – morning and afternoon, respectively.
Tilt, on the other hand, is the angle at which your roof is inclined – which is also the angle your solar panels adopt. This tilt should ideally match your geographic latitude to allow panels to absorb sunlight perpendicularly and maximize their efficiency.
Will the Energy My Roof Generates Be Enough to Cover My Energy Needs?
To know whether your roof’s solar output can meet your household’s energy needs, you’ll need to compare your system’s production to your electricity usage.
Earlier, we’ve discussed how you can calculate the potential energy generation of the solar system you plan to install.
Next, you should take a look at your recent monthly electric bill to find your average energy consumption in kilowatt-hours (kWh). Check this number against your system’s potential energy output.
Using the example of a 6 kW system that generates 30 kWh daily, you can estimate its monthly output by multiplying by 30 days: 30 kWh x 30 = 900 kWh.
If your household consumes around 900 kWh per month (close to the average energy use of a U.S. household), this system would likely meet your energy needs.
That said, I want to stress that your system’s not always going to produce exactly 30 kWh every day. Seasonal changes and daily weather patterns can affect peak sun hours, so energy production will vary throughout the year.
Can I Have ‘Too Many’ Solar Panels on My Roof?
If your roof has enough space to accommodate and properly fit the panels, having “too many” solar panels won’t typically be an issue at all. Still, here are a few things I’d suggest you bear in mind if you’re planning to add more roof-mounted panels:
Additional Cost
This is a no-brainer, but to really stress it: The more panels you install, the higher your upfront costs will be.
Your Roof’s Structural Capability
Newer roofs can, with no doubt, handle the lightweight nature of solar panels. But if your roof is nearing the end of its lifespan or its warranty period, I’d recommend considering a replacement first.
Even so, you shouldn’t worry too much about whether your existing roof can handle your solar panels or not. During the solar permitting process, professionals will investigate your roof’s suitability and let you know if major repairs or reroofing is needed.
System Compatibility
Solar systems are designed to match the capacity of their inverters. Connect too many panels to your inverter, and it may overload or even become damaged. By working with a certified solar installer, you can ensure your system is properly designed and sized to function optimally right from the start.
HOA Regulations
If you live in a community governed by an HOA, there may be restrictions on the number of panels you can install or where they can be placed. Make sure to check with them first before proceeding or better yet, seek the assistance of a solar installer who can work through such regulations for you.
Turn Your Roof Into a Solar Powerhouse
Anyone can install solar panels, but not everyone can do it in a way that maximizes energy production and lowers your utility bills year-round.
With Avail Solar, you’ll have a partner throughout the entire process. From design and permitting to installation and ongoing maintenance, we ensure your system works efficiently to save you money – without the hassle of contacting multiple people or worrying about the details. Get in touch with us to request a quote or discuss your home’s energy needs today!